My U.S. Pat. No. 5,785,523 describes an improved water line flushing and disinfecting system for a dental unit. The principal purpose of that prior art system is to clean all of several water using devices in a dental unit, not only a handpiece but also auxiliary components such as a syringe, scaler, basin and so on. The object is to provide a system integral with a dental unit which can be utilized to eliminate bacteria growth in all water lines of the unit. Periodically, however, it is necessary to purge the dental unit of all disinfectant and water and resume operation with fresh disinfectant and fresh water. The object of the present invention is to provide a detachable purge unit which can be taken from one dental unit to another to carry out periodically the removal of water from the unit, flushing of all water lines with fresh disinfectant, removal of that disinfectant and refilling of the lines of the unit with fresh water.